The present invention relates to a slit illuminating device adapted for use in the illumination of an exposure slit in a copier or the like.
Conventional slit illuminating devices comprising a tubular light source encircled by a reflector having a cylindrical reflecting surface of a conicoidal section are already disclosed for example in the U.S. Pat. Nos. 3,364,816 and 3,982,116; Japanese Patents Laid-Open Sho No. 50-61233, Sho No. 51-23725 and Sho No. 52-126241; and IBM Technical Disclosure Bulletins, Vol. 14, No. 11, April 1972, p. 3320, and Vol. 15, No. 2, July 1972, p.521-523.
Also, it is known that a compact copying apparatus can be obtained by employing, as the imaging system thereof, an imaging element array of a short focal length composed for example lenses of an axial length larger than the effective diameter thereof (hereinafter called bar lenses) as disclosed in the Japanese Patent Laid-Open Sho No. 53-122426 or of converging optical fibers for example known under the trade name of Selfoc wherein the refractive index decreases parabolically in the radial direction from the center thereof as disclosed in the Japanese Patents Laid-Open Sho No. 47-28057 and Sho No. 47-28058.
The present invention relates to an improvement in such conventional slit illuminating devices, the improvement being featured in that, in order to compensate for the reduction in size of a lower reflector resulting from the positional restriction of the imaging element array of a short focal length, in case of use of such array as the imaging system, a part of the upper reflector is provided with a function which is the same as that of the lower reflector thereby balancing the amounts of light illuminating the slit from the lower lateral directions thereof.